An arrangement in which an insert embedded at a predetermined position in a CFRP (carbon fiber-reinforced resin) is formed from a balsa core material, a metal insert member retained in the interior of the core material, and a CFRP covering layer covering the surfaces of the core material and the insert member is known from Patent Document 1 below.
An arrangement in which a floor panel of a cabin for a vehicle molded into a bathtub shape from a CFRP is formed by sandwiching a foam core between an upper wall and a lower wall, a washer is made to abut from the upper wall side against the upper end of a metal collar main body inserted into the floor panel from the lower wall side to the upper wall side, and a bolt extending through a seat rail and a washer is screwed into the collar main body to thus fix a seat to the floor panel is known from Patent Document 2 below.